Logarithmic amplifiers are much used in electronic systems where it is necessary to amplify signals having a vary large dynamic range, for example, signals extending over several decades of amplitude. The output from such logarithmic amplifier is an amplitude compressed signal, for example, the amplifier output signal amplitude may be compressed to only one third or one fifth of the dynamic range of the amplifier input signal amplitude. The result is a significant amplification of small input signals and only minimal amplification of large input signals. For example, it may be desired to compress an input signal amplitude with 60-90 db of dynamic range to an output signal amplitude with 15-30 db of dynamic range.
Logarithmic amplifiers are known and used in present day technology and described in articles, for example, by Nazoa-Ruiz et al., entitled, "A Logarithmic Distributed Amplifier, 1990 IEEE MTT-S Digest, Section R-30, pages 753-756, by Smith, entitled, A 0.5 to 4 GHz True Logarithmic Amplifier Utilizing Monolithic GaAs MESFET Technology, IEEE Transaction on Microwave Theory and Techniques, Vol. 36, No. 12, December 1988, pages 1986-1990, and by Oki et al., entitled High-Performance GaAs Heterojunction Bipolar Transistor Monolithic Logarithmic IF Amplifiers, IEEE Transaction on Microwave Theory and Techniques, Vol. 36, No. 12, December 1988, pages 1958-1965. Logarithmic amplifiers are also described in U.S. Pat. Nos. 4,885,483 and 4,908,529 to Aitchison which are incorporated herein by reference.
Despite the many practical applications of logarithmic amplifiers, they suffer from a number of disadvantages well known in the art. For example, they are often physically larger or consume more power or are more expensive to construct or require numerous adjustments or are unduly sensitive to component variations than is desired, or they exhibit combinations of the above and other deficiencies well known in the art.
At high frequencies (e.g. &gt;100 MHz), these problems become increasing difficult to avoid or overcome. For example, above about 100 MHz and especially above about 1 GHz, size, power consumption, sensitivity to device variations, difficulty of construction in Monolithic Microwave Integrated Circuit (MMIC) form, and the presence of off-chip components or the need for adjustment can severely limit their utility or performance.
Thus, a need for improved means and methods for logarithmic amplifiers continues to exist, especially logarithmic amplifiers capable of operating at high frequencies (e.g. &gt;100 MHz).